Flat wire conveyor belts are well known as exemplified by U.S. Pat. No. 2,872,023 to Bechtel. Generally, such belts comprise a plurality of tractive pickets or links which are formed to provide a plurality of longitudinally extending tractive members having slots therethrough. A plurality of tractive cross rods or pins extend through the slots for slideably interrconnecting the pickets.
The tractive members of each picket are connected by transversely extending connecting members which form with the tractive members a plurality of wedge-shaped segments. The segments defined by each picket may be nestably received within the segments defined by the longitudinally adjacent pickets, permitting the belt to collapse longitudinally.
When the belt travels around a lateral curve, it collapes longitudinally in a graduated manner across its width. The segments near the inner concave edge of the belt are nestably received further within the longitudinally adjacent segments than are the segments positioned progressively closer to the outer convex edge of the belt. As a result, when the belt travels around lateral curves, the entire tractive load of the belt is carried by a relatively few of the tractive members which are positioned nearest the outer edge.
When this occurs the tractive and connecting members forming the oute portion of each tractive picket are subjected to bending forces which cause elastic deformation or flexure of the picket, particularly at the junctures between the tractive and connecting members. The repeated imposition of such forces and the resulting elastic deformation frequently induces fatigue failure of the tractive links at the aforementioned junctures.
One solution to this fatigue failure problem is disclosed in U.S. Pat. No. 3,261,451 to Roinestad. This patent teaches that tapering the slots in the tractive members through which the cross rods extend, the elastic deformation experienced by the tractive pickets incident to travel of the belt around lateral curves will be distributed over a larger surface area of the pickets to reduce localized fatigue failure at the junctures between the tractive and connecting members. While this solution has proved satisfactory for some conveyor belt installations, it is not obviated to fatigue failure of tractive pickets in installations where the belt carries heavy tractive loads along a tortuous path.
Another solution is fatigue failure problem is disclosed U.S. Pat. No. Re. 27,690 to Roinestad. The solution disclosed in this patent is illustrated in FIGS. 1, 2 and 3 herein. A conveyor belt 10 comprises a plurality of transversely disposed the tractive pickets 12, a plurality of pivotal tractive cross rods 14 which interrconnect the tractive pickets and a plurality of substantially longitudinally disposed bar links 16 positioned adjacent tractive pickets along each edge of belt 10 and connected to the belt by the cross rods 14.
Tractive pickets 12 are fabricated from continuous strips of flat wire and are formed to provide a plurality of integral tractive wire members 18 which extend substantially longitudinally of belt 10. Adjacent ones of the tractive members are connected by integral connecting members 20 which extend substantially transversely of the belt. As shown in FIGS. 1 and 2, adjacent ones of the connecting members 20 extend between opposite ends of the tractive members 18 and the tractive members are slightly laterally inclined so that the tractive and connecting members of each tractive picket 12 form a plurality of alternating oppositely opening wedge-shaped segments 22.
Each tractive member 18 has a pair of longitudinally spaced, longitudinally extending slots 24 extending laterally therethrough it. Cross rods 14 extend through slots 24 to interconnect tractive pickets 12, and are slideable along slots 24 to permit belt 10 to collapse longitudinally, with the wedge-shaped segments 22 defined by one tractive picket being nestably received within the segments defined by the longitudinally adjacent tractive pickets, as shown in FIG. 3. Alternatively, the longitudinally spaced openings in the tractive members may comprise a single longitudinally extending slot and a circular hole, as shown in the aforementioned Bechtel patent, instead of the two longitudinally extending slots 24. In either instance, the belt is permitted to collapse longitudinally incident to the sliding of the cross rods 14 along the slots.
When belt 12 travels along a substantially straight path, as shown in FIG. 1, it extends longitudinally until cross rods 14 engage the bearing surfaces formed by the outer ends of the openings in tractive members 18. The outer ends of slots 24 extend slightly into the adjacent connecting members 20 so that when the belt is fully extended and cross rods 14 are engaged with the outer ends of the slots, the cross rods will abut the flat inner surfaces of the connecting members. As will be apparent, when the cross rods and tractive pickets are so disposed, the tractive load will be substantially equally distributed between the tractive members 18 of each tractive picket 12. The normal direction of belt travel is indicated by arrow 25 in FIG. 1. It is understood that the belt can just as easily travel in the opposite direction.
When belt 10 travels around a lateral curve, as shown in FIG. 3, it collapses longitudinally in a graduated manner across its width with segments 22 nearer the inner concave edge of the belt being nestably received further within the longitudinally adjacent segments than the segments progressively closer to the outer edge of the belt. As a result of such graduated collapsing, cross rods 14 slide away from the outer ends of slots 24 and the inner surfaces of the adjacent connecting members which are nearest the inner edge of the belt so that the tractive members 18 nearest the inner edge of the belt carry substantially none of the tractive load. Consequently, in the absence of bar links 16, the tractive members nearest the outer edge of the belt would carry substantially the entire tractive load. When this occurs tractive members 18 and connecting members 20 nearest the outer edge of the belt will be subjected to bending forces which cause tractive pickets 12 to elastically deform or flex, particularly at the junctures between the tractive and connecting members. Repeated elastic deformation of the tractive pickets induces fatigue failure at the aforementioned junctures, necessitating frequent replacement of the pickets.
This problem is substantially obviated by bar links 16, which, similarly to tractive pickets 12, preferably are fabricated from flat wire. As shown in the drawings, the bar links are substantially longitudinally disposed and are positioned adjacent tractive pickets 12 along each edge of belt 10. Bar links 16 each have a pair of longidinally spaced, longitudinally extending slots 26 extending laterally therethrough, through which cross rods 14 extend for connecting the bar links to the belt. The cross rods are transversely restrained by appropriate means, such as by enlarged head portions 27.
Alternatively, the longitudinally spaced openings in the bar links may comprise a single longitudinally extending slot and a circular hole, similar to the aforementioned alternative openings which may be employed in the tractive members. The slots and the bar links, similarly to the slots in the tractive members permit the belt to collapse longitudinally.
The bar links will carry a tractive load when the cross pins engage the bearing surfaces formed by the outer ends of the openings therein. This occurs when cross rods 14 engage the bearing surfaces formed by the outer ends of slots 26. The longitudinally spacing between the bearing surfaces of each bar link is correlated with the longitudinally spacing between the bearing surfaces of each tractive member so that when the belt travels along a substantially straight path, most of the tractive load of the belt will be carried by the tractive members, and, when the belt travels around a lateral curve, a substantial portion of the tractive load will be carried by the bar links disposed along the outer convex edge of the belt.
Generally, the spacing between the bearing surfaces of each bar link is at least as great, and preferably is greater than the spacing between the bearing surfaces of each tractive member. This longitudinal spacing differential need not be great and generally has been only a few thousandths of an inch. Bar links 16 significantly reduce fatigue failure in flat wire conveyor belts, however, over a period of time, the pitch of the tractive pickets, i.e. the spacing between the bearing surfaces of the tractive members increases. Since the pitch of the bar links is only a few thousandths of a inch greater than the picket pitch, the increase of the picket pitch results in the tractive pickets and the bar links assuming the same pitch. When this condition occurs, the flexing motion which the bar links are intended to eliminate begins to occur and fatigue failure can eventually result. When the outer portion of the tractive pickets takes on tractive load about a curve, particularly in high tractive tension modes of run, portion of the pickets cannot move with respect to the connecting rods. The vibration or movement caused by the motion of a central driving drum with respect to the inner edge of the belt is thus transmitted to the outer portion end of the picket and also contributes to fatigue failure. The present invention is specifically designed to further reduce the liklihood of fatigue failure by the use of edge bar links in combination with tractive pickets specifically designed to assure that tractive load is carried substantially by the edge bar links along the outer convex edge of the belt during travel about lateral curves, even after the pitch of the tractive pickets has increased over a period of time.